Double-flow scroll pump

Abstract

Double-flow scroll pump with a scroll casing (12) containing an orbiter (14) driven by a motor (16) to perform an orbiting motion, the motor (16) having a drive shaft (18) with an eccentric shaft section (20) that supports the orbiter (14). The orbiter (14) is axially displaceable on the eccentric shaft section (20). The orbiter (14) comprises a support plate (32), a first scroll (28) extending from a first side of the support plate and nested with a first stationary scroll (36) in the scroll casing (12) to form a first pumping stage (40), and a second scroll (30) extending from a second side of the support plate opposite the first and nested with a second stationary scroll (36) in the scroll casing to form a second pumping stage (42).wherein (i) one or more pressure equalization bores (44) are formed in the support plate (32) extending between the first and second sides of the support plate; and / or (ii) the support plate (32) is connected to the spiral casing via an anti-rotation device which prevents rotation of the orbiter (14) and applies a restoring force to the orbiter as a result of an axial deflection thereof; and / or (iii) an active axial magnetic bearing (60) is provided which is configured and operable to exert an axial magnetic force on the orbiter (14) for controlling its axial position.

Description

[0001] The present invention relates to a double-flow scroll pump, in particular a double-flow scroll vacuum pump, with a possibly multi-part spiral casing in which an orbiter, colloquially also referred to as a movable spiral component, is located, which is driven by a motor to perform an orbiting movement, for which purpose the motor has a drive shaft with an eccentric shaft section that carries the orbiter.

[0002] A scroll pump is a positive displacement pump that compresses against atmospheric pressure and can be used, among other things, as a compressor. A scroll vacuum pump can be used to create a vacuum in a container to which the scroll vacuum pump is connected via its gas inlet.

[0003] Scroll pumps are also known as spiral vacuum pumps or spiral conveying devices. The pumping principle underlying a scroll pump is fundamentally known from the prior art and is therefore only briefly explained below.

[0004] A pump stage of a scroll pump comprises two nested or interlocked spiral cylinders, for example, shaped as involutes, which are hereinafter referred to simply as spirals. Each spiral has at least one spiral wall, which is attached to a support plate or formed integrally with it, wherein the outer turns of the spiral, for example the two or three outermost turns of the spiral, can be formed by wall sections that are each located at a constant circumferential distance from the center of the spiral. Even though these wall sections do not strictly constitute spiral sections, in the context of the present invention they are considered part of the spiral and referred to as turns thereof.

[0005] The spirals are nested within each other in such a way that the two spirals of each pump stage enclose crescent- or sickle-shaped volumes in sections. One of the two spirals is fixed within the pump's spiral casing, while the other spiral, along with its support plate, can be moved along a circular path via an eccentric drive. This is why this spiral, together with its support plate, is also referred to as the orbiter. The movable spiral thus performs a so-called centrally symmetrical oscillation, which is also known as "wobbling" or "orbiting." A crescent-shaped volume enclosed between the spirals migrates increasingly radially inward within the spirals during the orbiting of the movable spiral. This migrating volume conveys process gas from a radially outer gas inlet to a gas outlet located in the center of the spiral.

[0006] Although double-flow scroll pumps are generally known, single-flow or unidirectional scroll pumps have become established on the market. These typically feature a so-called tip seal at the free end of each scroll. This tip seal is designed to seal the axial gap between the free end of the scroll and an adjacent section of the scroll casing or the orbiter's support plate. However, these tip seals wear out over time and must therefore be replaced periodically. Due to the associated maintenance effort, single-flow scroll pumps have become the preferred choice, as replacing the tip seal in these pumps only requires removing the scroll casing cover and the stationary scroll inside to access the tip seals.

[0007] Although double-flow scroll pumps with Tipseal seals are generally known, they have not been able to establish themselves so far due to increased maintenance costs, as these pumps require a considerable amount of maintenance for replacing the respective Tipseal seals.

[0008] Tip-seal-less scroll pumps are also known; however, these require very small axial gaps (less than 40 µm) between the free axial end of the scroll and the adjacent wall sections, across all operating conditions. This proves particularly difficult to achieve with single-flow scroll pumps, as the axial gap can change temperature-related under different operating conditions. This is primarily due to the orbiter being located at the free end of the drive shaft and beyond its bearings. Furthermore, the orbiter's position at the free end of the drive shaft means that the shaft, like a cantilever, is subject to greater elastic bending deformations, which can negatively affect the gaps in the pump system.

[0009] In view of the difficulties explained above, the invention is therefore based on the objective of providing a Tipseal-free scroll pump in which the requirements for the axial gaps to be maintained can be met under all operating conditions.

[0010] To solve this problem, a double-flow scroll pump, in particular a double-flow scroll vacuum pump, is proposed for the first time according to the invention, which is characterized by the features of claim 1.

[0011] The double-flow scroll pump according to the invention has, in a conventional manner, a scroll housing in which an orbiter is located, driven by a motor to perform an orbiting motion. For this purpose, the motor has a drive shaft with an eccentric shaft section on which the orbiter is rotatably mounted. As is usual in a double-flow design, the orbiter comprises a carrier plate, a first scroll extending from a first side of the carrier plate, which is nested with a first stationary scroll in the scroll housing to form a first pumping stage, and a second scroll extending from a second side of the carrier plate opposite the first, which is nested with a second stationary scroll in the scroll housing to form a second pumping stage.

[0012] According to the invention, the orbiter is not only rotatable but also axially displaceable on the eccentric shaft section, for example by means of a plain bearing or a needle bearing. This allows the orbiter to be mounted precisely in the center of the spiral casing during assembly. Furthermore, should the axial gaps on one side of the support plate change during pump operation, these changes can be compensated for by means of suitable mechanisms (i), (ii), (iii), which will be described in more detail below.

[0013] One of the mechanisms in question (i) can be implemented by providing one or more pressure equalization bores in the support plate, extending between the first and second sides of the support plate. If, for example, different pressure conditions arise in the two pump stages on either side of the support plate, leading to an axial displacement of the orbiter, such pressure differences can be equalized by the pressure equalization bores in question. As a result of this pressure equalization, the orbiter is again subjected to equal forces on both sides, ultimately centering it axially.

[0014] A second of the mechanisms in question (ii) can be implemented by means of an anti-rotation device, via which the orbiter's support plate is connected to the spiral casing. This anti-rotation device is designed to prevent rotation of the orbiter, which would otherwise occur due to the orbiting motion of the orbiter, and to apply an axial restoring force to the orbiter as a result of any axial displacement. The anti-rotation device can, for example, be a spring-like or elastic component that, due to its elastic properties, tends to counteract axial displacement of the orbiter, thus always forcing it back into its central initial position.

[0015] A third of the mechanisms in question (iii) can be implemented by means of an actively controlled axial magnetic bearing, which is set up and can be operated in such a way that an axial magnetic force is exerted on the orbiter.

[0016] Although the three aforementioned mechanisms (i), (ii), (iii) are based on different mechanisms of action, each of them is based on the same idea: to ensure the orbiter returns to its original position in the event of an unwanted axial displacement. Accordingly, the individual mechanisms (i), (ii), (iii) can also complement each other without the effect of one mechanism being negated by that of another.

[0017] In the following, specific embodiments of the double-flow scroll pump according to the invention will be discussed, whereby further embodiments may also result from the dependent claims, the description of the figures and the figures themselves.

[0018] According to one embodiment, the drive shaft can be rotatably mounted in the spiral housing on both sides of its eccentric shaft section by means of a rolling bearing, in particular a ball bearing. Because the eccentric shaft section, and thus the orbiter, is supported on both sides, and not only on one side as in a conventional single-flow scroll pump, the eccentric shaft section can only deform minimally in the radial direction due to bending. This allows the axial gaps of the double-flow scroll pump according to the invention to be kept small under any operating conditions.

[0019] According to a further embodiment, the two spirals of the orbiter can be identical in design. Preferably, the first spiral can have a rotational offset relative to the second spiral, preferably 180°. Additionally or alternatively, the direction of rotation of the first spiral can be opposite to that of the second spiral. For example, if the first spiral is a right-handed spiral when viewed from the first side of the support plate, the second spiral is also a right-handed spiral when viewed from the second side of the support plate, or a left-handed spiral when viewed from the first side of the support plate.Although any imbalances can be largely compensated for by the essentially identical design of the two spirals, any remaining imbalances can be further reduced by the rotation angle offset of the two spirals and / or by the different direction of rotation of the spirals.

[0020] To counteract any imbalances, according to a further embodiment, the orbiter's spirals can also be designed differently, with the two spirals differing in particular with regard to their number of turns and / or the distance between adjacent turns. The spirals could also differ from each other with regard to their number of turns and / or wall thickness in order to achieve a specific ratio with respect to pressure distribution and / or imbalance.

[0021] According to a further embodiment, the one or more pressure equalization bores may be positioned in the carrier plate and / or have a shape, in particular a size, such that, during the orbiting movement of the orbiter, each pressure equalization bore, viewed axially, is always located on the same side of a wall section of the stationary spirals or always between adjacent winding sections. The pressure equalization bores are thus positioned and / or designed such that, viewed axially, they are not swept over by the spirals during the orbiting movement of the orbiter, in order to prevent backflow of the process gases towards the gas inlet of the pump.If required, the pressure equalization bores can each be equipped with a backflow preventer in the form of, for example, a spring valve, in particular a check valve, which only opens above a predetermined pressure difference.

[0022] As regards the anti-rotation device, according to one embodiment it can comprise several spring elements spaced evenly apart along the outer circumference of the carrier plate, which are attached on the one hand to the outer circumference of the carrier plate and on the other hand in the spiral housing or to the same.

[0023] Specifically, according to one embodiment, each spring element can, for example, comprise a curved spring arm in the form of a leaf spring, which is attached at a first end to the outer circumference of the support plate and at a second end to the spiral housing. Each spring arm can have a mounting section at its second end that bears at least indirectly against and is attached to an axially oriented end face of the spiral housing. Preferably, the mounting section bears indirectly against the inner end face via a spacer. By selectively choosing spacers of different thicknesses, the axial position of the orbiter, and thus the respective axial gap at the free end of the spirals, can be precisely adjusted.

[0024] As an alternative to designing the spring elements as spring arms, each spring element, according to a further embodiment, can comprise an elastic plate element extending in the plane of the support plate and outwards from the outer circumference of the support plate. In this embodiment, it is preferably provided that a radially outer radial section of each plate section indirectly abuts the inner end face via a spacer, in order to allow the axial position of the orbiter to be precisely adjusted via the spacers, even in this embodiment.

[0025] Regardless of whether the spring elements are designed as spring arms or elastically resilient plate elements, according to a further preferred embodiment, each spring element has an axial stiffness that is greater than its radial stiffness. Due to the low radial stiffness of the spring elements, they do not impair, or only minimally impair, the orbiting motion of the orbiter, which has a positive effect on the required drive power of the pump.

[0026] According to another possible embodiment, the anti-rotation mechanism may comprise an elastic membrane which is attached on one side to the outer circumference of the carrier plate and on the other side to the spiral housing. Preferably, the membrane may have several longitudinally spaced elongated holes oriented axially, with a fastening element extending through each elongated hole for attaching the membrane to the carrier plate and / or to the spiral housing.Since membranes from different batches may exhibit slight dimensional deviations, which can lead to the orbiter not being positioned exactly in the center of the spiral housing, such dimensional deviations can be compensated for by the elongated holes in question, as the elongated holes make it possible to mount the orbiter exactly in the center of the spiral housing despite any dimensional deviation of the respective membrane.

[0027] According to yet another embodiment, the active axial magnetic bearing may have two magnetic coils spaced apart axially, forming a gap. A tab element, extending radially inwards from the outer circumference of the carrier plate, extends into this gap and is made of a magnetizable material, for example iron, or of a permanent magnetic material. By selectively controlling the magnetic coils, the axial position of the orbiter can thus be adjusted, particularly during pump operation. For this purpose, the axial position of the carrier plate must be detected using suitable sensors, and the magnetic coils can then be controlled based on this position.

[0028] According to a further embodiment, the orbiter may have an emergency running element on each side of the carrier plate, made of a low-friction material, in particular PTFE or another dry lubricant. This element runs against a stationary housing section during axial deflection of the orbiter, before the free end of one of the stationary spirals contacts the carrier plate. Instead of a low-friction material, the emergency running elements can also be designed, for example, as ball bearings to prevent the spirals from running against the carrier plate during axial deflection of the orbiter. The emergency running elements can also be defined by raised areas with specific tight tolerances, which are machined to achieve these tight tolerances.

[0029] According to yet another embodiment, the first spiral, the second spiral, the first stationary spiral, and / or the second stationary spiral of the orbiter may have a soft wear-resistant coating, which may be located, in particular, at the free end of the respective spiral. Such a soft wear-resistant coating can serve to compensate for manufacturing tolerances of the individual spirals and largely close the respective axial gap before the pump is initially commissioned. Only during the initial commissioning of the pump is the wear-resistant coating then ground off, thus creating a minimal axial gap. This compensates for any manufacturing or assembly tolerances of the components and results in minimal gap ratios between the orbiter and the spiral casing.The wear coating in question can be, for example, a fluoropolymer such as Xylan® Defric, which is applied to the respective spiral with a thickness between 10 and 200 µm and preferably with a thickness of 50 to 150 µm.

[0030] To counteract temperature-related changes in the axial gaps caused by differing thermal expansion rates between the orbiter and the spiral casing, a further embodiment provides for the spiral casing to be made of a material with a higher coefficient of thermal expansion than the orbiter. In particular, the spiral casing may be made of an aluminum material, such as an aluminum alloy, and the orbiter of steel. Since the orbiter is generally exposed to higher temperatures than the spiral casing, this ensures that the spiral casing and the orbiter expand to approximately the same extent, thereby maintaining the axial gaps essentially constant under various operating conditions.

[0031] The invention will now be described in the following by way of example only, with reference to the drawings in which: Fig. 1 schematically illustrates a first embodiment of a scroll pump according to the invention; Fig. 2 schematically illustrates a second embodiment of a scroll pump according to the invention; Fig. 3 schematically illustrates a third embodiment of a scroll pump according to the invention; Figs. 4-7 illustrate different configurations of the orbiter of a scroll pump according to the invention in different views; Figs. 8 and 9 illustrate the axial positioning of the orbiter using spring arms as an anti-rotation device; Figs. 10 and 11 illustrate the axial positioning of the orbiter using an elastic diaphragm as an anti-rotation device; Fig. 12 illustrates the axial positioning of the orbiter using elastic plate elements as an anti-rotation device; Fig. 13 shows a representation to illustrate an emergency running device in the form of two emergency running elements.

[0032] TheFig. 1Figure 1 schematically shows a first embodiment of a scroll pump 10 according to the invention, which comprises an orbiter 14 located in a spiral casing 12 and driven by a motor 16, which may be located in a separate casing section. Specifically, the motor 16 has a drive shaft 18, which includes an eccentric shaft section 20 on which the orbiter 14 is axially displaceable by means of needle bearings (not shown here), although plain bearings may also be used instead of needle bearings. The drive shaft 18 is rotatably mounted in the spiral casing 12 by means of two ball bearings 22, which are located on either side of the eccentric shaft section 20.Due to the eccentric mounting of the orbiter 14 on the eccentric shaft section 20, the orbiter 14 is driven by the motor 16 to perform an orbiting motion, whereby process gas is conveyed along a fluid flow path in a manner known per se between a pump inlet 24 and a pump outlet 26 of the scroll pump 10.

[0033] According to the invention, the scroll pump 10 is designed as a double-flow pump, for which purpose the orbiter 14 has two spirals 28, 30: The first spiral 28 extends from a first side of the carrier plate 32 of the orbiter 14 and is connected to or integrally formed with it, whereas the second spiral 30 extends from the second side of the carrier plate 32 opposite the first side and is connected to or integrally formed with it. The first spiral 28 is nested with a first stationary spiral 34, which extends axially from the spiral housing 12. Similarly, the second spiral 30 is nested with a stationary second spiral 36, which also extends axially from the spiral housing 12.The first spiral 28, together with the first stationary spiral 34, forms a first pumping stage 40, while the second spiral 30, together with the second stationary spiral 36, forms a second pumping stage 42, which is flow-wise connected in parallel to the first pumping stage 40. Process gas drawn in through the pump inlet 24 is thus conveyed radially inwards through the two pumping stages 40 and 42, from where it exits the scroll pump 10 via the pump outlet 26. To allow the process gas conveyed by the first pumping stage 40 to reach the pump outlet 26, the support plate 32 has a passage 38 near its center, through which the process gas conveyed by the first pumping stage 40 can enter the second pumping stage 42 and from there reach the pump outlet 26.

[0034] Instead of designing the scroll pump 10 with only a single pump outlet 26, the scroll pump 10 could also have two pump outlets 26, with one pump outlet being assigned to the first pump stage 40 and a second pump outlet to the second pump stage. In this case, the passage 38 in the carrier plate 32 could be omitted, since the process gas pumped by each pump stage 40, 42 could leave the scroll pump 10 via the pump outlet assigned to the respective pump stage 40, 42.However, the design of the scroll pump 10 with only a single pump outlet 26 and the passage 38 in the carrier plate 32 can prove to be advantageous, since in this case ballast gas, which is directed into the first pump stage 40 via an inlet opening to prevent undesirable condensation phenomena inside the pump, can pass through the passage 38 into the second pump stage 42, so that no separate inlet openings are needed to introduce ballast gas into the second pump stage 42.

[0035] Again Fig. 4As can be seen from the diagram, several pressure equalization bores 44 are formed in the support plate 32, extending between the first and second sides of the support plate 32. Contrary to the illustration, these bores can be of different sizes, at least partially. In particular, the pressure equalization bores 44 can have different diameters, at least partially. The pressure equalization bores 44 thus equalize the pressure between the two pump stages 40, 42, ensuring that the orbiter 14 is always subjected to symmetrical forces in the axial direction, as is desirable to prevent axial displacement of the orbiter 14. Although not shown here, the pressure equalization bores 44 can each be equipped with a non-return valve, for example, a spring-loaded valve, in particular a check valve, which opens only above a predetermined pressure differential.If ballast gas is introduced via separate inlet openings, it may prove advantageous to place the pressure equalization bores 44 near these inlet openings so that the ballast gas can be ideally distributed on both sides of the support plate 32.

[0036] In the embodiment of the Fig. 4 A total of 8 pressure equalization bores 44 are provided, all of which are located on a straight line that perpendicularly intersects the drive shaft 18. The individual pressure equalization bores 44 are located between the individual turns of the two spirals 28, 30, with the embodiment shown here having only a single equalization bore 44 located centrally between each turn.

[0037] Alternatively, several pressure equalization bores 44 can be provided between the respective turns of the spirals 28, 30, which may also be of different sizes. The pressure equalization bores 44 can be positioned in the support plate 32 such that, during the orienting movement of the orbiter 14 in the axial direction, each pressure equalization bore 44 is always located on the same side of a wall section of the stationary spirals 34, 36. The pressure equalization bores 44 can thus be positioned precisely so that the stationary spirals 34, 36 do not overlap the pressure equalization bores 44, thereby preventing backflow of the process gases towards the gas inlet of the pump.

[0038] According to the presentation of Fig. 6The two spirals 28, 30 can be fundamentally identical in design, particularly with regard to the number of turns and the distance between adjacent turns of the spirals 28, 30. However, to minimize undesirable imbalances, the first spiral 28 can be designed with an angular offset relative to the second spiral 30, preferably 180°. Additionally or alternatively, as shown in the illustration, Fig. 7 It is intended that the two spirals 28, 30 differ from each other with respect to their direction of rotation, although they are identical in form when viewed individually. Thus, viewed from the same side of the support plate 32, one of the spirals 28, 30 can be configured as a left-handed spiral and the other as a right-handed spiral.

[0039] To prevent rotation of the orbiter 14 as a result of the drive by the motor 16, the support plate 32 is designed according to the illustrations of the Figs. 8 and 9 The spiral housing 12 is connected via several curved spring arms 46. The spring arms 46 are formed by leaf springs or bending beams, which are attached at one end to the outer circumference of the support plate 32 and at the other end to the spiral housing 12. For this purpose, each spring arm 46 has a fastening section 48 at its other end, which is attached to an axially oriented inner end face (see Figs. 2 u. 9) of the spiral housing 12 indirectly rests against it via a spacer 52, which is inserted between the end face 50 and the mounting section 48. By specifically selecting spacers 52 of different thicknesses, the axial position of the orbiter 14 can thus be precisely determined during the assembly of the scroll pump 10.

[0040] The described anti-rotation device in the form of spring arms 46 not only prevents rotation of the orbiter 14; rather, the spring arms 46 exert an axial restoring force on the orbiter 14 if it should shift axially in an undesirable manner during operation of the scroll pump 10. As with the previously described pressure equalization bores, the spring arms 46 thus ensure that the orbiter 14 automatically re-centers itself axially within the spiral casing 12 if it should have shifted axially due to operational reasons.

[0041] Instead of implementing the previously described anti-rotation device by means of several spring arms 46 in the form of leaf springs, the anti-rotation device can be implemented according to Fig. 12for example, they can also be formed by several elastic plate elements 54 spaced apart from one another in the circumferential direction of the support plate 32, which extend in the plane of the support plate 32 and extend radially outwards from its outer circumference. In the embodiment of Fig. 12 The elastic plate elements 54 have an essentially triangular shape, with their respective radially outer corner sections resting against the inner end face 50 of the spiral casing 12 via a spacer (not visible), in order to precisely determine the axial position of the orbiter 14.

[0042] Another embodiment of the anti-rotation device is described in the Figs. 10 and 11The anti-rotation device is formed by an elastic membrane 56 with a substantially U-shaped cross-section, which is attached on one side to the outer circumference of the support plate 32 and on the other side to a radially outwardly projecting circumferential surface of the spiral housing 12. Alternatively, according to an embodiment not shown, the membrane 56 could extend substantially in the plane of the support plate 32 and from the outer circumference of the support plate 32 to a radially circumferential and inwardly projecting inner circumferential surface of the spiral housing 12, as shown in the Fig. 11 is schematically illustrated with dashed lines.

[0043] In order to also in the embodiment according to the Figs. 10 and 11To enable the axial position of the orbiter 32 to be determined via the anti-rotation device, the diaphragm 56 can have several longitudinally spaced elongated holes 58, which are aligned axially. Suitable fastening elements extending through the elongated holes 58 allow the diaphragm 56 to be attached to the carrier plate 32 or to the spiral housing 12, with the elongated holes 58 enabling fine adjustment of the orbiter 14 relative to the spiral housing 12.

[0044] The following refers to the Fig. 3Another embodiment of the scroll pump 10 according to the invention is described, in which an active axial magnetic bearing 60 is used to counteract unwanted axial deflection of the orbiter 14. The axial magnetic bearing 16 comprises two axially spaced magnetic coils 62, which are attached to the inside of the spiral housing 12. In contrast, a tab element 64 is provided on the outer circumference of the support plate 32, extending radially into the space between the two magnetic coils 62. The tab element 64 is made of a magnetizable material such as iron or of a permanent magnetic material, so that the axial position of the support plate 32, and thus that of the orbiter 14, can be adjusted by selectively energizing the magnetic coils 62 if unwanted axial deflections of the orbiter 14 occur during pump operation.

[0045] Since contact between the free ends of the spirals 28, 30 and the spiral housing 12 as well as between the stationary spirals 34, 36 and the support plate 32 should be prevented in any case, the orbiter 14 can be arranged according to the illustration of the Fig. 13On both sides of the carrier plate 32, an emergency running element 66 is provided, with these emergency running elements 66 projecting slightly beyond the spirals 28, 30 in the axial direction. The emergency running elements 66 thus ensure that, in the event of axial deflection of the orbiter 14, the spirals 28, 30, 34, 36 do not run into opposing wall sections. Instead, in the event of axial deflection of the orbiter 14, the emergency running elements 66 first run into a stationary housing section, thereby preventing further deflection of the orbiter 14 and thus any potential running of the spirals 28, 30, 34, 36 against the inside of the housing or the carrier plate. The emergency running elements 66 can be annular discs made of PTFE or another dry lubricant. Alternatively, the emergency running elements can also be formed by ball bearings or thrust bearings, in particular thrust plain bearings. Reference symbol list

[0046] 10 Scroll pump 12 Spiral housing 14 Orbiter 16 Motor 18 Drive shaft 20 Eccentric shaft section 22 Ball bearing 24 Pump inlet 26 Pump outlet 28 First spiral 30 Second spiral 32 Support plate 34 First fixed spiral 36 Second fixed spiral 38 Passage 40 First pump stage 42 Second pump stage 44 Pressure equalization bores 46 Spring arms 48 Mounting section 50 End face 52 Spacer 54 Elastic plate element 56 Membrane 58 Slotted holes 60 Axial magnetic bearing 62 Magnetic coils 64 Tab element 66 Emergency running element

Claims

1. Double-flow scroll pump (10), in particular a double-flow scroll vacuum pump, with a scroll casing (12) in which an orbiter (14) is located, which is driven by a motor (16) to perform an orbiting motion, wherein the motor (16) has a drive shaft (18) with an eccentric shaft section (20) which supports the orbiter (14), wherein the orbiter (14) is mounted to be axially displaceable on the eccentric shaft section (20) and comprises a support plate (32), a first spiral (28) extending from a first side of the support plate (32) and nested in the scroll casing (12) with a first stationary spiral (34) to form a first pumping stage (40), and a second spiral (30) extending from a second side of the support plate (32) opposite the first side and nested in the scroll casing (12) with a second stationary spiral to form a second pumping stage (42). (36) is nested in the spiral casing (12),wherein: (i) one or more pressure equalization bores (44) are formed in the support plate (32) extending between the first and second sides of the support plate (32); and / or (ii) the support plate is connected to the spiral casing (12) via (32) a rotation-prevention device which prevents rotation of the orbiter (14) and applies a restoring force to the orbiter (14) as a result of an axial deflection thereof; and / or (iii) an active axial magnetic bearing (60) is provided which is configured and operable to exert an axial magnetic force on the orbiter (14) for controlling its axial position.

2. Double-flow scroll pump (10) according to claim 1, wherein the drive shaft (18) is rotatably mounted in the spiral housing (12) on both sides of its eccentric shaft section (20) by means of a rolling bearing (22).

3. Double-flow scroll pump (10) according to claim 1 or 2, wherein the orbiter (14) is mounted on the eccentric shaft section (20) so as to be displaceable in the axial direction by means of a sliding bearing or a needle bearing.

4. Double-flow scroll pump (10) according to one of the preceding claims, wherein the two scrolls (28 30) of the orbiter (14) are identical in design, wherein it is provided in particular that (i) the first scroll (28) has a rotational angular offset relative to the second scroll (30), which is preferably 180°, and / or (ii) that the direction of rotation of the first scroll (28) is opposite to the direction of rotation of the second scroll (30).

5. Double-flow scroll pump (10) according to one of claims 1 to 3, wherein the two spirals (28, 30) of the orbiter (14) are designed differently, wherein the two spirals (28, 30) differ in particular with respect to their number of turns and / or with respect to the distance between adjacent turns.

6. Double-flow scroll pump (10) according to one of the preceding claims, wherein the one or more pressure equalization bores (44) are positioned in the carrier plate (32) and / or have such a shape, in particular size, that each pressure equalization bore (44) is always located on one and the same side of a wall section of the stationary spirals (34, 36) when viewed in the axial direction during the orbiting movement of the orbiter (14).

7. Double-flow scroll pump (10) according to one of the preceding claims, wherein the anti-rotation device comprises several spring elements spaced apart from one another along the outer circumference of the carrier plate (32), which are attached on one side to the outer circumference of the carrier plate (32) and on the other side in the spiral housing (12), wherein it may preferably be provided that the spring elements are spaced evenly apart from one another along the outer circumference of the carrier plate (32).

8. Double-flow scroll pump (10) according to claim 7, wherein each spring element comprises a spring arm (46) which is attached at a first end to the outer circumference of the carrier plate (32) and at a second end to the spiral housing (12), wherein each spring arm (46) has at its second end a fastening section (48) which bears at least indirectly against and is attached to an axially oriented inner end face (50) of the spiral housing (12), wherein it is preferably provided that the fastening section (48) bears indirectly against the inner end face (50) via a spacer (52).

9. Double-flow scroll pump (10) according to claim 7, wherein each spring element comprises an elastic plate element (54) extending in the plane of the support plate (32) and extending radially outwards from the outer circumference of the support plate (32), wherein it is preferably provided that a radially outer edge section of each plate element (54) indirectly abuts the inner end face (50) via a spacer (52).

10. Double-flow scroll pump (10) according to claim 7, 8 or 9, wherein each spring element is stiffer in the axial direction than in the radial direction.

11. Double-flow scroll pump (10) according to one of claims 1 to 6, wherein the anti-rotation device comprises an elastic diaphragm (56) which is attached on one side to the outer circumference of the carrier plate (32) and on the other side to the spiral housing (12), wherein it is preferably provided that the diaphragm (56) has several elongated holes (58) spaced apart from each other in the circumferential direction and which are aligned in the axial direction, wherein a fastening element for fastening the diaphragm (56) to the carrier plate (32) and / or to the spiral housing (12) extends through each elongated hole (58).

12. Double-flow scroll pump (10) according to one of the preceding claims, wherein the active axial magnetic bearing (60) has two magnetic coils (62) spaced apart from each other in the axial direction forming a gap, wherein a tab element (64) made of a magnetizable or permanent magnetic material extends radially outwards from the outer circumference of the carrier plate (32) into the gap, and the axial position of the carrier plate (32) can be adjusted by selectively supplying current to the magnetic coils (62).

13. Double-flow scroll pump (10) according to one of the preceding claims, wherein the orbiter (14) has on both sides of the carrier plate (32) an emergency running element (66) made of a low-friction material, in particular of PTFE or of another dry lubricant, which, in the event of an axial deflection of the orbiter (14), runs up against a stationary housing section before the free end of one of the stationary spirals (34, 36) touches the carrier plate (32).

14. Double-flow scroll pump (10) according to one of the preceding claims, wherein the first spiral (28), the second spiral (30), the first stationary spiral (34) and / or the second stationary spiral (36) has a wear coating, in particular made of a dry lubricant, wherein the wear coating preferably has a thickness of 10 - 200 µm and particularly preferably a thickness of 50 - 150 µm.

15. Double-flow scroll pump (10) according to one of the preceding claims, wherein the scroll casing (12) is made of a material having a different, in particular a higher, coefficient of thermal expansion than the material of which the orbiter (14) is made, wherein it is particularly provided that the scroll casing (12) is made of an aluminum material and the orbiter (14) is made of steel.

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